This invention relates generally to inflatable passive restraint systems for use in vehicles for restraining the movement of a seated occupant during a collision and, more particularly, to an improvement in the structure for housing and positioning a gas generator and an inflatable bag in the vehicle.
Safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems" and particularly those restraint systems incorporating inflatable bags or cushions, as well as the use of such systems in motor vehicles have been the subjects of much discussion as the desirability of the use of such passive restraint systems has gained general acceptance.
In general, air bag module assemblies of the prior art generally include three basic components: 1) a cushion or air bag that is inflated with gas such as when the vehicle encounters a sudden deceleration, 2) an inflator which upon actuation serves to provide the gas used to inflate the air bag, and 3) a reaction canister which typically functions as a structural housing supporting both the inflator and the air bag while providing a mounting base for installation of the assembly in a vehicle and direction to the inflation gases resulting from the inflator.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated with gas, e.g., an "inflatable bag" or, commonly referred to as an "air bag", when the vehicle encounters sudden deceleration, such as in a collision. During deployment, the gas with which the bag is typically filled is an inert gas, e.g., nitrogen. In such systems, the inflatable bag is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the restraint system, gas is discharged from an inflator to rapidly inflate the bag. The bag can then serve to restrain the movement of the vehicle occupant as the collision proceeds.
Vehicular inflatable restraint systems generally include multiple crash sensors generally positioned about or mounted to the frame and/or body of the subject vehicle and serve to sense sudden decelerations by the vehicle. In turn, the sensor sends a signal to an inflatable bag module/assembly strategically positioned within the riding compartment of the vehicle to actuate deployment of the air bag. In general, an inflatable bag provided for the protection of a vehicle driver, i.e., a driver side air bag, is mounted in a storage compartment located in the steering column of the vehicle. Whereas, an inflatable bag for the protection of a front seat passenger, i.e., a passenger side air bag, is typically mounted in the instrument panel/dash board of the vehicle.
Typical inflatable passive restraint systems make use of an air bag module which generally includes an outer reaction housing or canister, commonly referred to as a "reaction can" or, more briefly, as a "can". The reaction canister generally serves to support or contain other components of the air bag module system, including what is referred to as a "air bag inflator" or, more briefly, as an "inflator", or, alternatively, as a "generator". The inflator, upon actuation, acts to provide the gas to inflate the bag.
In the past, typical pyrotechnic air bag inflators comprised a steel housing having walls of a thickness related to the gas production characteristics of the pyrotechnic material housed therein, with the walls of conventional inflators required to be relatively thick to contain the maximum gas pressure exhibited under high ambient temperature conditions.
Emphasis on weight reduction in automobiles, however, has created a need, and a demand, for a lighter weight passenger side inflatable passive restraint system. A most significant reduction in the weight of the system can be achieved through the utilization of a low weight material such as aluminum or an aluminum alloy rather than a heavy steel material, as used in previous structures, for inflatable restraint system inflator structures.
The use of aluminum for air bag inflators is disclosed, for example, in commonly assigned U.S. Pat. No. 4,547,342, issued Oct. 15, 1985 to Adams et al., and U.S. Pat. No. 4,561,675, issued Dec. 31, 1985 to Adams et al.
U.S. Pat. No. 5,346,251 discloses the inclusion of a V-shaped arcuate stress concentration groove along a wall of an inflator to result in structural failure of the air bag inflator pressure vessel in the event of over pressurization.
However, because of the relatively high pressures generated in conventional inflators, e.g., pyrotechnic inflators commonly produce pressures in the range of about 1500-3000 psi, the walls of such inflators are typically fabricated of relatively thick material to provide additional strength thereto.
In addition, in conventional air bag module assemblies, the inflator is typically housed within a walled reaction canister. This housing structure provides protection for the gas generator and the inflatable bag until the time of deployment of the latter and also acts to absorb the loads generated by the deployment of the bag. Typically, these loads are large and unless sufficiently absorbed can cause damage to the vehicle including, in the case of a passenger side assembly, damage to the dash panel. Thus, it has been a practice in the prior art to use heavyweight structures, particularly steel structures, for housing and positioning an inflator, particularly an inflator for a passenger side assembly, in order to prevent or minimize such damage. As will be appreciated, the use of a thick walled inflator housed within a walled reaction housing typically results in an assembly of greater weight than is optimally desired.
However, commonly assigned U.S. Pat. No. 4,941,678, Lauritzen et al., issued Jul. 17, 1990, discloses a lightweight housing canister assembly having a design avoiding such bell mouthing deformation. The assembly includes a body part, such as made of by continuous aluminum extrusion. The assembly further includes a tether strap, at the mouth inside the bag. The tether strap serves to: 1) restrict the loading of the reaction canister that is positioned transversely thereto and 2) retain the spreading forces at the mouth of the canister upon bag deployment. This allows the use of a lighter section at the mouth of the canister and eliminates the need for reinforcing flanges along the sides of the canister, which flanges would undesirably increase the weight of the assembly. The structural arrangement of the Lauritzen et al. patent, however, complicates the manufacturing and assembling operations, and moreover, does not allow installation of the inflator as a last operation in the assembly of the module.
Air bag assembly structures fabricated of such light weight materials typically will not experience problems in ordinary use wherein, during the event of a collision, the ignition agent is ignited, followed by the igniting of the gas generant to generate inflation gas. However, the mechanical strength of such lighter weight materials is lowered when overheated to a high temperature, such as when subjected to a high temperature environment, such as a bonfire. This problem stems from the fact that at a temperature in excess of about 300.degree. F. (149.degree. C.), the pyrotechnics of pyrotechnic-containing gas generators commonly automatically ignite. In this temperature range, the aluminum of the housing structure degrades and tends to rupture or burst, which in turn can result in the projection of pieces and/or fragments in various directions. This problem is typically not encountered with structures that employ steel since steel does not degrade until a much higher temperature of about 1100.degree. F. (593.degree. C.) is reached. Thus, the use of aluminum, in place of steel, while serving to reduce the weight of the assembly typically results in a structure having a lower internal pressure capability. This lower internal pressure capability could be hazardous in a high temperature environment such as a reaction canister structure in a module assembly might be subjected to in the event of a fire whether in storage, in transit, or after installation in a vehicle.
Thus, there is a need and a demand for inflatable restraint system structures, specifically a reaction canister structure, which provides for the safe release of energy therefrom, such as produced by an inflator housed therein when exposed to extreme heat conditions, e.g., a fire, without forming or projecting metal fragments into the vehicle interior.
In addition, inflatable passive restraint systems are commonly installed in vehicles of a variety of different sizes and shapes. Further, there are a variety of different types of inflators such as pyrotechnic, stored gas or hybrid inflators, for example and which inflators can take a variety of shapes and/or sizes as the inflators are specifically designed for particular applications.
As a result, there is a need for a reaction canister structure having applicability in a wide variety of applications and in which an inflator selected from a wide variety of inflator devices can be utilized. That is, there is a need for a reaction canister structure that is capable of a more widespread or universal utilization and applicability.
Further, as reaction canisters are commonly fabricated using formed and/or welded steel, such fabrication techniques are not conducive to the economical and effective incorporation therein of various desired features, such as various mounting or attachment preparations, for example, in particular vehicular inflatable restraint system design applications. Thus, there is a need and a demand for an improved structural arrangement which is conducive to the economical and effective incorporation of various such desired features for particular vehicular inflatable restraint system design applications.
Still further, an increasing emphasis on weight reduction in automobiles has created a need and a demand for an improved structural arrangement which permits the more widespread usage of lighter weight assemblies.
Yet still further, there is a need and a demand for a light weight air bag module assembly structural arrangement which is not subject to undesired fragmentation when subjected to extreme temperature conditions, such as a bonfire.
Thus, there is a need and a demand for an improved reaction canister for use in an air bag module, particularly for the passenger side of a vehicle. In particular, there is a need and a demand for an air bag reaction canister construction which facilitates and permits the greater use of light weight, temperature sensitive materials, such as of aluminum and various aluminum alloys, where previously only heavier, relatively temperature insensitive materials, such as steel, could be used due to concerns such as of material fragmentation when exposed to extreme heat conditions, such as from a fire.